Example usage for org.apache.commons.math.stat.descriptive.moment Variance increment

Introduction

In this page you can find the example usage for org.apache.commons.math.stat.descriptive.moment Variance increment.

Prototype

@Override
public void increment(final double d) 

Source Link

Document

If all values are available, it is more accurate to use #evaluate(double[]) rather than adding values one at a time using this method and then executing #getResult , since evaluate leverages the fact that is has the full list of values together to execute a two-pass algorithm.

Usage

From source file:org.basketball.MyKMeansPlusPlusClusterer.java

/**
 * Get a random point from the {@link Cluster} with the largest distance variance.
 *
 * @param clusters the {@link Cluster}s to search
 * @return a random point from the selected cluster
 *///from w  w w . ja v a 2s.c  o m
private T getPointFromLargestVarianceCluster(final Collection<Cluster<T>> clusters) {

    double maxVariance = Double.NEGATIVE_INFINITY;
    Cluster<T> selected = null;
    for (final Cluster<T> cluster : clusters) {
        if (!cluster.getPoints().isEmpty()) {

            // compute the distance variance of the current cluster
            final T center = cluster.getCenter();
            final Variance stat = new Variance();
            for (final T point : cluster.getPoints()) {
                stat.increment(point.distanceFrom(center));
            }
            final double variance = stat.getResult();

            // select the cluster with the largest variance
            if (variance > maxVariance) {
                maxVariance = variance;
                selected = cluster;
            }

        }
    }

    // did we find at least one non-empty cluster ?
    if (selected == null) {
        throw new ConvergenceException(LocalizedFormats.EMPTY_CLUSTER_IN_K_MEANS);
    }

    // extract a random point from the cluster
    final List<T> selectedPoints = selected.getPoints();
    return selectedPoints.remove(random.nextInt(selectedPoints.size()));

}

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